negotiated 

This is a low-level utility for correctly parsing the HTTP content negotiation headers. It doesn't interpret the parsed values in any way, except for ensuring that they are syntactically correct.

Installation

``bash
npm install --save negotiated
`

Usage

`js
const negotiated = require('negotiated');

const best = Array.from(negotiated.languages('fr;q=0.4, ja-JP;q=0.2, de-DE;q=0.7, en;q=0.5'))
.reduce((a, b) => a.weight >= b.weight ? a : b);

console.log(best.language); // => "de-de"
`

This package exports six functions:

- mediaTypes(): parses the Accept header, emitting { type, params, weight, extensions }
- charsets(): parses the Accept-Charset header, emitting { charset, weight }
- encodings(): parses the Accept-Encoding header, emitting { encoding, weight }
- languages(): parses the Accept-Language header, emitting { language, weight }
- transferEncodings(): parses the TE header, emitting { encoding, params, weight }
- parameters(): parses the params and extensions found above, emitting { key, value }

Each of the exported functions takes a string as the only argument. An iterator is returned, which parses one comma-separated item at a time. If the input string is invalid (according to RFC 7230 or RFC 7231), an error will be thrown mid-iteration.

Examples

#### Iterating over the Accept-Encoding header

`js
const negotiated = require('negotiated');

for (const { encoding, weight } of negotiated.encodings('gzip;q=0.5, my-custom-encoding;q=1')) {
if (weight > 0.8) console.log(${encoding} is desired);
}

// => "my-custom-encoding is desired"
`

#### Parsing media parameters

`js
const negotiated = require('negotiated');

const [{ params }] = Array.from(negotiated.mediaTypes('application/json; CHARSET="utf-8"'));

console.log(Array.from(negotiated.parameters(params))); // => [{ key: 'charset', value: 'utf-8' }]
``